共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary Lower Mississippian Waulsortian mounds in the Sacramento Mountains grew on a south-dipping homoclinal ramp at depths ranging
from approximately 110 to 250 m, a setting in which nutrient sources and pathways are poorly understood in ancient carbonate
depositional systems. Lithologic, biotic, and chemical data suggest that the mounds grew in an area on the ramp within a dysoxic
oxygen minimum zone (OMZ) resulting from the concentration of organic matter below a thermocline. The abundance of organic
matter there, perhaps a consequence of upwelling, enhanced the productivity of the major sediment contributors to the mounds—sponges,
pelmatozoans, bryozoans, and heterotrophic carbonate-producing microbes.
The siting and growth of individual mounds within the OMZ is best explained by two factors. One is the positive low-relief
intra-ramp topography on and around which the mounds grew. The other is that nutrient supply for carbonate producing microbes
was concentrated at the sites of mounds growth by internal waves on the pycnocline coincident with the thermocline. The internal
waves mixed the nutrient-rich water of the OMZ with the better-oxygenated adjacent water mass, stirred the substrate and resuspended
organic matter so that it was more available for the primarily suspension-feeding macrofauna both above and below the pycnocline,
and generated local vertical mixing. Because of initial intra-ramp topography and subsequently increased relief as the mounds
grew, internal waves focused and localized these processes, thus enhancing carbonate production at individual mound sites
in a positive feed-back loop. 相似文献
2.
Summary The marine Paleogene of the Tremp Basin in the Central Southern Pyrenees corresponds to four depositional sequences which
are related to global eustatic third order cycles (Tejas A 2.3–2.6). Associated transgressive and downlap surfaces coincide
with boundaries of biozones. Lowstand systems tracts consist of estuarine and braid delta systems. Transgressive and highstand
systems tracts are composed of carbonate banks and reefs.
Slow thrust-induced changes of the basin topography conditioned the basic type and the areal distribution of carbonate highstand
and clastic lowstand systems. Rapid relative sea level changes controlled the activity and internal dynamic of the depositional
systems. E-W directed blind thrust anticlines are covered during highstand periods by carbonate fringing banks withNummulites bars. N-S orientation of thrust anticlines leads to the evolution of reef-dominated barrier banks and shelf lagoonal homoclinal
ramps. On-bank transport of carbonate sands dominates during transgressions, off-bank transport during highstand periods.
Continuous thrusting during the Ilerdian caused angular unconformities only in combination with relative sea level fall. Sequence-internal
onlap configurations result from contemporaneous tectonic tilting. Fourth order carbonate bank margin cycles contain well
developed lowstand tracts due to increased subsidence rates. Fourth order flooding surfaces are marked by paleosoil horizons
at their landward continuation. 相似文献
3.
The hemi-pelagic Tafilalt Ridge separating the Maider Basin from the Tafilalt Basin developed progressively from an Early
Devonian homoclinal ramp, through a Middle Devonian ramp-slope stage of moderate topography, to a mature cephalopod ridge
during the Late Devonian and formed a spur-like element extending from the southern shallow-water Maider Platform to the broader
northern hemi-pelagic Tafilalt Platform. During the Middle Devonian, thick lowstand aprons were shed onto the ridge-slope
from an active mid-ramp carbonate factory in the south (Maider Platform). The shallow-water derived sediments first by-passed
the central paleohigh, but then onlapped the ridge during start of sea-level rise. The allodapic limestones (storm-induced
turbidites, tempestites, and debrites) of the aprons consist of large parts or entirely of reworked lithic peloids. The lithic
peloids are interpreted as the main foundation of all micritic lithofacies types in the distal ramp locations, including those
on the hemi-pelagic cephalopod ridge. Lateral facies transition of allodapic limestones into nodular cephalopod limestones
on the ridge suggests the latter originate from allodapic beds and were subsequently transformed into nodular limestones by
bioturbation, early diagenesis, and the faunal input from a hemi-pelagic community. Iron-rich hardgrounds formed on the ridge
during major regressive phases as a result of increased winnowing by the wave-base and correlate with siliciclastic turbidite
deposition on the slope. The hardgrounds can be correlated with hiatuses on the Tafilalt Platform, which formed a broader
hemi-pelagic swell to the north. During the Late Devonian, the southern Maider Basin carbonate factory became unproductive
or disappeared, and a ridge facies of truly hemi-pelagic autochthonous limestones developed. Allodapic deposits on the slope
were shed from the ridge itself at this time but did not form well-defined aprons. 相似文献
4.
Based on microfacies analyses and sedimentological data, 17 facies are identified within the Middle Miocene carbonates at Siwa Oasis in the northern Western Desert of Egypt. These facies are attributed to five main facies belts. Within these facies and facies belts, five foraminiferal assemblages are recognized. A depositional model relates the reported facies and biofacies to a down-dip depositional profile of an inner to middle carbonate ramp. The facies of the peritidal to restricted lagoon (facies belt 1) and the less-restricted lagoon (facies belt 2) were deposited in the inner ramp behind the barrier/beach shoal facies belt 3. Basinward, lime mudstone of facies belts 4 and 5 accumulated in a proximal to distal middle ramp, respectively. The depositional evolution involved three stages, which are strongly controlled by tectonics and eustatic sea-level changes. The first stage comprises the transgressive Lower Miocene clastic-dominated fluvial facies of the Moghra Formation. The second stage heralds the deposition of the Langhian inner-ramp carbonate and shale facies of the basal Oasis Member of the Marmarica Formation under a relatively high stand of sea level, constrained clastic influx and climate warming. The final stage is represented by Langhian to Serravallian mid-ramp carbonate-dominated facies of the Siwa Escarpment and El Diffa Plateau members under fluctuating sea level, and a westward restriction in clastic supply and water turbidity. 相似文献
5.
Partha Pratim Chakraborty 《Facies》2011,57(2):331-349
The Neoproterozoic Lakheri Limestone (LL) Member of Vindhyan Supergroup, central India, interpreted as a low-gradient homoclinal
ramp, contains a wide range of signatures indicating syn-sedimentary basinal extension and compression. Whereas features like
intraformational truncation (slide) surfaces of varying geometry, creep and bedding translation manifest the phases of extension,
the compressional events are registered in bed-confined thrusts and outcrop-scale folds. A wide range of outcrop and microscopic
deformational features are associated with the sliding events, the expressions of which vary based on their relative position
with respect to the slide surface (over- or underlying) and the degree of built-up pore water pressure. The detached sediment
mass often evolved in the form of mass flows with rheology varying between cohesive debris flow and low-density turbidity
current. In particular, operation of reflected turbiditic flows is suggestive of irregular depositional substrate, induced
by curvilinear syn-sedimentary slides in otherwise low-gradient distal shelf platformal setting. The present study intends
to relate the observed extensional and compressional features of LL succession with the flexural response of early rifted
Vindhyan basement under reversing in-plane stress in its post-rift depositional history. Bipolar NE–SW orientation of the
slide planes is well consistent with the proposed rifted configuration of Vindhyan basement. Centimeter- to decimeter-deep
slide detachments and equally thick mass-flow beds are indicative of relatively deeper level of necking during the early syn-rift
phase of Vindhyan history. 相似文献
6.
Due to a long-term transgression since the Early Cambrian, an extensive shallow-water carbonate platform was developed in the entire Tarim Basin (NW China). During the deposition of the Yingshan Formation (Early-Middle Ordovician), a carbonate ramp system was formed in the intrashelf basin in the Bachu-Keping area of the western basin. Four well-exposed outcrop sections were selected to investigate their depositional facies, cycles, and sequences, as well as the depositional evolution. Detailed facies analyses permit the recognition of three depositional facies associations, including peritidal, semi-restricted subtidal, and open-marine subtidal facies, and eleven types of lithofacies. These are vertically arranged into meter-scale, shallowing-upward peritidal, semi-restricted subtidal, and open-marine subtidal cycles, in the span of Milankovitch frequency bands, suggesting a dominant control of Earth’s orbital forcing on the cyclic sedimentation on the platform. On the basis of vertical facies (or lithofacies) and cycle stacking patterns, as well as accommodation changes illustrated graphically by Fischer plots at all studied sections, six third-order depositional sequences are recognized and consist of lower transgressive and upper regressive parts. In shallow depositional settings, the transgressive packages are dominated by thicker-than-average, shallow subtidal cycles, whereas the regressive parts are mainly represented by thinner-than-average, relatively shallow subtidal to peritidal cycles. In relatively deep environments, however, the transgressive and regressive successions display the opposite trends of cycle stacking patterns, i.e., thinner-than-average subtidal cycles of transgressive packages. Sequence boundaries are mainly characterized by laterally traceable, transitional zones without apparent subaerial exposure features. Good correlation of the long-term changes in accommodation space inferred from vertical facies and cycle stacking patterns with sea-level fluctuations elsewhere around the world suggests an overriding eustatic control on cycle origination, platform building-up and evolution during the Early-Middle Ordovician, although with localized influences of syndepositional faulting and depositional settings. 相似文献
7.
Dr. Ermanno Danese 《Facies》1999,41(1):41-54
Summary The development of carbonate ramp depositional systems in the Neogene of the Mediterranean Region represents a widespread
feature so far analysed in several papers. It is striking to note that the evolution of upper Miocene carbonate ramps, characterized
by the presence of coralgal bioherms, highlights the events leading to the Messinian salinity crisis. The coralgal bioherms
of preevaporite Messinian age exhibit fossil assemblages indicating marine waters with normal salinity, whereas stromatolitic
and microbial encrustations underline the deterioration of the environment during the Messinian salinity crisis. Maiella Mountain
is a broad carbonate massif located in Abruzzo (Central Italy). The late lower Oligocene-Messinian part of its stratigraphic
succession consists of stacked non-tropical carbonate ramp deposits related to third and higher order sequences. The investigations
performed in the southernmost portion of the massif allowed to recognize a complete fourth order carbonate depositional sequence
on a homoclinal ramp of pre-evaporite Messinian age. The presence of small coralgal patch reefs and overlaying microbial encrustations
is significant. A transect exhibits the stratigraphic framework of the area. The data show how local parameters play a notable
role in the development of these deposits. 相似文献
8.
Summary The factors controlling the localization and growth of Lower Mississippian Waulsortian mounds have been difficult to establish
because of limited exposure of individual mounds and mound-bearing platforms in western Europe, where the Waulsortian facies
have been studied most intensively. Mounds on the Lower Mississippian homoclinal ramp of the Lake Valley Formation in the
Sacramento Mountains, however, are exposed exceptionally well at platform, outcrop, and mound scales in an area roughly 5
km by 20 km, and provide the opportunity to better understand these aspects of Waulsortian mounds.
Mounds occur in the northern 2/3 of the essentially continuous 32 km dip transect of the ramp. Mounds grew in an outer ramp
setting below wave base, predominantly in the deeper part of the photic zone. Mounds range from broad composites of laterally
back-stepping subunits on the shallow part of the ramp to taller and more vertically stacked composite structures down-ramp.
The composite nature of the mounds is documented by distinct stratal units that have characteristic facies and geometries
common to mounds throughout the transect. As a result, mound growth and form can be described in terms of several primary
controlling parameters—submarine topography, water circulation (upwelling of nutrients and oxygen rich waters; oxygen deficient
bottom waters), light penetration and the distribution of phototrophic microorganisms, and fluctuations in accommodation.
Episodic mound growth is documented by diastems bounding the stratal units within the mounds as well as by the long-established
useage of Alamogordo, Nunn, and Tierra Blanca phases of mound growth, correlative with the contemporaneous level-bottom units.
However, mound growth that has been correlated with the level-bottom Nunn Member in reality took place during the late stage
of deposition of the Alamogordo Member, and nondeposition or erosion occurred on the mounds during deposition of the Nunn
Member.
Mounds in the shallower (northern) part of the ramp grew primarily on the margins of a broad, low, intra-ramp topographic
high, which had been defined previously from facies and isopach trends in underlying strata. Both the margins and the irregular
topography of the high are reflected in the distribution, growth geometries, and facies patterns of the mounds, and by the
facies and thickness trends of the strata enclosing the mounds. The siting of individual mounds on the shallower part of the
ramp was controlled by local topography on and along the margins of the intra-ramp high. Mound growth along the margin began
at or just behind local highs, retrograded onto the intra-ramp high, and then prograded onto the basinward side of the initial
mound.
The lesser height and more pronounced backstepping of mounds on the shallower part of the ramp, in contrast to mounds that
grew more vertically and with less back-stepping down ramp suggest that growth and overall morphology were also controlled
by accommodation. 相似文献
9.
The Permian–Triassic boundary and basal Triassic shallow-marine successions were studied and correlated in sections of two
structural units in Hungary (Transdanubian Range and Bükk units). Core sections in the Transdanubian Range unit recovered
inner ramp deposits whereas outcrops in the Bükk unit expose deposits of the deeper ramp area of the western Tethys. The inner
ramp section (studied ca. 10 m in thickness) is characterized by a succession of dolomites overlain by bioclastic limestones,
peloidal grainstones (which recorded the biotic decline) and oolites with finely crystalline limestone interlayers. The deeper
ramp section (studied ca. 15 m in thickness) is characterized by a succession of bioclastic limestones and marlstones, mudstone
beds (recording the first biotic decline), the ‘boundary shales’ (recording the second biotic decline and the stable carbon
isotope marker), mudstones with wackestone laminae, and stromatolite boundstones. Accordingly, oolite formation and microbial
micrite precipitation represent carbonate sedimentary responses of end-Permian mass extinction on the carbonate shelf. In
both successions, mudstones predominate the upsection, suggesting a relative sea-level rise. The succession of the deep ramp
area exhibits a continuous sediment accumulation and the diagenesis here was influenced by marine and marine-derived pore
water. The δ13C curve shows a continuous change towards more negative values, starting in bioclastic limestones, followed by a sharp symmetric
negative peak at the second biotic decline that is a chemostratigraphic marker of the boundary event. Facies and microfacies
trend of the inner ramp carbonates in the Transdanubian Range unit exhibits close similarities to that found in many South
Alpine sections. Relict peloidal deposits, formed cemented submarine hardground substrate, indicate the extinction level.
Sedimentary and diagenetic features of the overlying oolite bedset revealed slightly different depositional environments in
the two studied Transdanubian Range unit sections. Petrography of the oolites highlighted shallow burial diagenetic alterations
which includes marine cementation, marine-burial replacement and dolomitization. A lack of the specific negative peak in the
δ13C values is most likely due to the multiple redeposition events of the sedimentary grains. This led to the conclusion that
the deeper ramp deposits (e.g., in Bükk unit) have greater potential for recognizing trends in processes, affecting the marine
environments and related to the end-Permian mass extinction, at the western Tethys. 相似文献
10.
《Comptes Rendus Palevol》2013,12(3):137-148
A study of the ammonite assemblages from the “Oolithe ferrugineuse de Bayeux” Formation of Bajocian age is presented herein. The section at the locality of Maizet shows a high level of stratigraphic condensation, and taphonomic reworking is common within the sequence. All the ammonites being studied are classified herein as having been reworked, transported or displaced on the sea-floor prior to burial, and as such, are determined taphonomically as being resedimented or reelaborated fossil elements. Seven evidences of reelaboration within the sequence under investigation are detailed here. The palaeontological units, so-called taphorecords, characterized by distinctive taphonomic features, are used to directly or indirectly assign beds to biochronostratigraphic units. In addition, identification of taphorecord relationships regarding successive or contemporaneous deposition allows their registratic succession and order of depositional events to be inferred. The latter may be deduced on the basis of bed succession or by reference to stratigraphical intervals that now are only represented in the stratigraphic column by fossils. Deposition by tractional currents and winnowing is indicated by sharp bed-base and by reworked fossil elements. Biochronostratigraphic correlation with other sections of the inland Bajocian successions in the Calvados area (Bretteville, Feuguerolles) highlights a common depositional evolution that may be related to an eastward-deepening carbonate ramp. 相似文献
11.
Ivan Martin-Rojas Roberta Somma Francisco Delgado Antonio Estévez Alessandro Iannace Valeria Zamparelli 《Facies》2012,58(2):297-323
A litho-biostratigraphic analysis has been carried out in the Gador-Turon unit of the Sierra de Gador (Alpujarride complex,
Betic Cordillera, SE Spain). The Triassic succession of this unit is composed of a lower meta-detrital formation overlain
by an upper meta-carbonate formation divided in six members. In the latter, a Ladinian–Carnian-rich fossil association has
been found (foraminifers, algae, bivalves, microproblematica, trace fossils). Facies analysis has enabled the recognition
of 22 facies of platform origin. This succession accumulated as a subsiding margin-type carbonate platform with homoclinal
ramp geometry (Anisian?–Ladinian) evolving into a fault-block-type platform with a steeper-margined geometry (Ladinian–Carnian).
Slope deposits of this latter platform show a prism-like geometry with progradational patterns and include syn-sedimentary
structures associated with normal faults capped by younger beds. The results of the present research indicate that the architecture
of the platform studied has been controlled mainly by climate and oceanic factors during the development of the ramp, and
by syn-sedimentary extensional tectonics during the development of the steeper-margined platform. The Ladinian–Carnian tectonic
activity was probably also responsible for the siliciclastic input and the shift to a mixed terrigenous-carbonate platform. 相似文献
12.
The Upper Ordovician (Sandbian; late Whiterockian to Mohawkian) Bromide Formation of south-central Oklahoma was deposited along a distally steepened ramp that descended into the Southern Oklahoma Aulacogen (SOA). It provides an unparalleled opportunity to examine a spectrum of marine facies that extended from back ramp peritidal settings to the center of the basin. The depositional history and environmental context of the unit are reconsidered using lithofacies analysis and the characterization of sequence stratigraphic patterns at a variety of hierarchical scales. Inner-ramp (above fair weather wavebase; FWWB) lithofacies suggest deposition in a range of environments: tidal flat, lagoon, shoreface, semi-restricted shallow subtidal, and bioclastic shoal. Middle-ramp environments between FWWB and storm wavebase (SWB) are thick and faunally diverse, and consist of rhythmically bedded marls, wackestone, packstone, and shales. Outer-ramp environments (below SWB) are represented by either fissile tan-green shale or thin-bedded carbonate mudstone and shale. Ramp stratigraphy, facies associations, and bounding surfaces suggest that three third-order depositional sequences are present in the Bromide. They demonstrate the transition from a clastic-dominated ramp in the late Whiterockian to a carbonate-dominated ramp in the Mohawkian, and show that the deposition of the Bromide was considerably more complex than the simple transgressive–regressive cycle traditionally used to describe accommodation dynamics in the basin. Meter and decameter-scale cycles (high-frequency sequences) are a common motif within the depositional sequences, and the Corbin Ranch Submember records an important peritidal succession prior to a major sequence boundary with the overlying Viola Springs Formation. New correlations based on measured sections, outcrop gamma-ray profiles, and subsurface well-logs document a novel pattern where the middle Bromide depositional sequence 2 (Mountain Lake Member) expanded down-ramp, whereas the succeeding carbonate-dominated sequence 3 (Pooleville Member) was progressively removed down-ramp. This demonstrates the existence of a major, regionally angular unconformity at the base of the Viola Springs Formation that has implications for basin evolution. Other implications include the validation of high-frequency sequences as a model for elementary cycles in mixed carbonate-siliciclastic systems and, more regionally, documentation of a new depositional sequence at the Turinian–Chatfieldian stage boundary. 相似文献
13.
Summary A local intraplatform basin developed in the Gartnerkofel-Zielkofel area of the Carnic Alps (southern Carinthia, Austria)
during the Middle Triassic (Ladinian). This basin was filled with a transgressive basinal sequence composed of the Uggowitz
Formation and overlying Buchenstein Formation. At the northwestern slope of the Gartnerkofel, the platform carbonates of the
Schlern Dolomite interfinger with the Buchenstein Formation, causing the formation of two depositional sequences.
The Uggowitz Formation consists of the Uggowitz Breccia and the Kühweg Member. Sediments of the Uggowitz Breccia were formed
by different types of gravity induced processes. The Kühweg Member is a thin sequence of silt-and fine-grained sandstones
which were deposited in a slope to basin margin environment by turbidity currents. The overlying Buchenstein Formation consists
of hemipelagic to pelagic limestones of Fassanian age with intercalated pyroclastic rocks (Pietra verde). Nodular limestones
were deposited under slow rates of accumulation during a relative sea-level highstand. The uppermost Buchenstein Formation
is composed of hemipelagic limestone beds with intercalated graded calcarenites and breccias of platform-derived debris, showing
characteristics features of a fore-reef slope of the prograding Schlern Dolomite.
Uggowitz Formation and basal Buchenstein Formation are interpreted as a transgressive systems tract, nodular limestones from
the middle part of the Buchenstein Formation mark an early highstand systems tract, forereef slope sediments of the upper
Buchenstein Formation formed during the beginning regression of a late highstand systems tract, the basal part of the overlying
Schlern Dolomite probably reflects a lowstand systems tract.
The intercalated bedded limestone facies within the Schlern Dolomite is characterized by large, platform derived blocks, slump
structures, breccia beds, graded calcarenites and hemipelagic limestones indicating a forereef slope environent. This intercalated
facies belongs to the Buchenstein Formation and interfingers with the Schlern Dolomite. Conodonts from this intercalated slope
facies point to Late Fassanian age. Therefore, the two Middle Triassic depositional sequences of the Gartnerkofel area can
be correlated with the depositional sequences ‘Ladinian 1’ and ‘Ladinian 2’ of the Dolomites, proposed byDe Zanche et al. (1993). A brief comparison with the basinal sequences of similar age of the karawanken Mountains and the Carnia is
presented. 相似文献
14.
Ramon Mercedes‐Martín Luis A. Buatois 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2021,54(1):4-25
The timing of recovery after the end‐Permian mass extinction has been a matter of debate, with some authors favouring a more rapid faunal recovery during the Early Triassic and others considering a more protracted biotic reestablishment spanning until the Middle Triassic. In this work, we investigated the lowermost Middle Triassic (Ladinian) carbonate deposits in the Catalan Basin to evaluate the potential environmental mechanisms and evolutionary constrains involved in the kilometre‐scale predominance of microbialites and the low‐diversity and high‐density Planolites association in a low‐latitude epicontinental setting. The studied sedimentary succession records the development from a low‐gradient, homoclinal microbial‐dominated carbonate ramp evolving towards a slightly inclined swell‐dominated type. Sedimentological analysis suggests that facies heterogeneity was controlled by pulses of syn‐rift tectonic activity, which compromised Peri‐Tethyan basin connectivity, reducing palaeobathymetry gradients. Although the monospecific nature of the studied trace‐fossil association may reflect the delayed recovery after the end‐Permian mass extinction, this is inconsistent with widespread, relatively high‐diversity ichnofaunas in carbonates elsewhere in the region. Since other Ladinian basins were characterized by the recurrence of microbial carbonates, low‐diversity ichnoassemblages and limited skeletal production, we hypothesize that shallow and restricted carbonate ramp settings harboured limited ecological complexity and widespread opportunistic colonization of the sediment when compared to coeval open marine locations. 相似文献
15.
Thomas Olszewski 《Facies》1996,35(1):81-103
Summary The Iola Limestone is the open-marine, carbonate portion of a Midcontinent cyclothem. It represents the transgressive and
highstand systems tracts of a stratigraphic sequence.
The sequence begins with a type 1 sequence boundary at the base of the Chanute Shale, which underlies the Iola. This surface
can be recognized by the presence of a paleosol and as much as 15 m of incision. Part of the Chanute is probably an estuarine
valley-fill package and represents the lowstand systems tract.
The lowest member of the Iola Limestone is the Paola Limestone Member. Its base is sharp and locally has a thin shell lag.
This contact is the transgressive surface and represents the onset of open-marine, clear-water carbonate sedimentation. It
is a ravinement surface cut by a winnowing environment that appears as a ‘kink’ in the base-level surface. Landward of this
‘kink’, sediment accumulated to a subaerial base-level, but seaward of it sediment did not accumulate above a subtidal threshold
probably controlled by wave base. Facies formed during regression also show the influence of a ‘kink’ in base-level. The Paola
itself is the lower part of the transgressive facies tract.
Overlying the Paola is the Muncie Creck Shale Member; its lower part is black and fissile, contains phosphate nodules, no
unequivocally benthic fossils, and no discernible trace fossils. However, this facies is not present everywhere; in much of
southeastern Kansas and just north of Kansas City, Missouri, it has been removed by submarine erosion. The only clues that
this facies was ever deposited are reworked diagenetic phosphate nodules that occur as a lag on a hardground on top of the
Paola. Where black shale and the immediately overlying, relatively unfossiliferous gray shale have been preserved, they are
overlain by a shelly lag that incorporates bored and encrusted micritic cobbles-strong evidence of reworking. This erosional
surface is interpreted as the maximum flooding surface. Such an interpretation suggests that the black shale formed during
sea-level rise and coastal transgression rather than at sea-level highstand. This is further supported by geochemical properties
of Midcontinent black shales.
Overlying the maximum flooding surface are a thin gray shale (within the Muncie Creek) and the Raytown Lime-stone Member.
In southern Kansas, the limestone contains an extensive phylloid-algal mound. In the subsurface, the elongate Raytown mound
is perpendicular to the outcrop belt; it directly overlies a Precambrian structural element called the Bourbon arch, suggesting
subtle tectonic control. In northern Missouri and in Nebraska, the upper Raytown contains carbonate tidal-flat deposits. The
existence of these two facies suggests that the Raytown was deposited while base-level was stable rather than during base-level
drop. The aggradational algal mound built into a positive sea-floor feature and did not shift position through the duration
of the cycle. Progradational carbonate tidal flats had the chance to develop in the northern part of the field area; if base-level
had been dropping, rapid regression would likely not have permitted accumulation of this facies at the top of the limestone.
Coarse-grained deposits, an oncolite in southern Kansas and bioclastic packstones and grainstones in northern Kansas, indicate
that the mound aggraded up to a subtidal base-level, presumably controlled by wave base. The carbonate tidal flats, on the
other hand, filled accommodation space up to a subaerial base-level as they prograded out over this surface. There must have
been two base-levels—one subtidal and the other subaerial—connected by the previously mentioned base-level ‘kink’ at the coastline.
The Lane Shale, typically gray-green and silty, overlies the Iola. In a core from northern Missouri, the Lane Shale directly
overlying the Raytown contains clay slickensides and a breccia of ‘fitted’ carbonate clasts, indicating subaerial exposure
and qualifying the base of the Lane Shale as the top boundary of the Iola sequence.
In northwestern Missouri, the Iola changes from a relatively clay-free limestone to mostly dark-gray, calcareous mudrocks
with thin shell stringers. This represents a part of the basin dominated by clastic input.
Stratigraphic interpretation implies that the Muncie Creek black shale formed during accommodation space increase and shoreline
transgression. This is consistent with recent geochemical studies of Midcontinent black shales. This lithology formed as inland
peat swamps underwent ravinement and organic matter was flushed onto the shelf. An influx of nutrients and plant material
made available by sea-level rise and transgression while sediment was trapped in nearshore accommodation space was the primary
cause of sediment starvation and anoxia in the basin. 相似文献
16.
Seafloor erosion and sea-level change: Early Jurassic Blue Lias Formation of central England 总被引:1,自引:1,他引:0
Minor bedforms within the mudstone-dominated Early Jurassic Hettangian Saltford Shale Member (Liasicus up to Angulata Chronozone) of the Blue Lias Formation in central England, indicate weak seafloor erosion in a mid to outer ramp setting. Distal storm flows below maximum storm wave base are proposed as the most likely generative mechanism for silty scour and gutter casts that enclose concentrations of well-preserved schlotheimiid ammonites and arthropod trace fossils. Within the upper part of the Saltford Shale (probably Angulata Chronozone), a discrete layer of reworked and bioencrusted limestone nodules signifies an episode of more persistent seafloor erosion. The immediately overlying strata, transitional to the Hettangian–Sinemurian Rugby Limestone Member, are relatively bioturbated and feature fossils of macrobenthos, as well as shell concentrations resembling relatively proximal storm beds. This suggests that the reworked nodule horizon marks sea-level fall, rather than stratigraphic condensation associated with sediment starvation. The biostratigraphic evidence raises the possibility that this erosional episode correlates with a mid-Angulata Chronozone hiatus documented from the Wessex Basin, southwest England. Equally however, it could be linked to contemporaneous movement on one or more nearby faults, affecting the southern part of the English East Midlands Shelf. 相似文献
17.
A detailed facies study of Early Permian strata within NE Svalbard reveals a fundamental change of the depositional setting, from a restricted-marine, warm-water carbonate platform to an open-marine, temperate-water, mixed siliciclastic-carbonate ramp. The uppermost strata of the Gipshuken Formation (Templet and Sørfonna members; Sakmarian–early Artinskian?) consist of microbialites (algal mats), mudstones, bioclastic/peloidal limestones, carbonate breccias and Microcodium facies reflecting peritidal platform areas and supratidal sabkhas. A mixed heterozoan/reduced photozoan assemblage indicates temperate-water conditions within neighboring deeper, open-marine mid-platform areas, while warm-water conditions still prevailed within inner platform zones. In contrast, the lowermost strata of the overlying Kapp Starostin Formation (Vøringen Member; late Artinskian?–Kungurian) show a fully heterozoan biotic assemblage reflecting temperate water conditions within open-marine, storm-dominated, nearshore to transitional offshore areas of a mixed carbonate-siliciclastic ramp. The Vøringen Member comprises three facies associations, which form a shallowing-upward sequence subsequent to an initial transgression. The sediments reflect bryozoan bioherms in most distal areas, followed by stacked tempestites of sandy brachiopodal shell banks and Skolithos piperocks, grading into broad sand flats in most proximal areas of the inner ramp. The above environmental change is regarded as a regional event taken place across the entire shelf along the northern margin of Pangea and is attributed to paleoclimatic, paleoceanographic, as well as paleogeographic changes, possibly related to the overall northwards drift of the supercontinent. An abrupt increase in terrigenous input coinciding with this change is ascribed to the uplift of a new local source area, probably to the north or east of the investigation area. 相似文献
18.
Lubomir F. Jansa 《Palaeogeography, Palaeoclimatology, Palaeoecology》1974,15(4):233-244
U-shaped burrows identified as the trace fossil Arenicolites occur in the Cambro-Ordovician Cow Head Group, a series of thin-bedded limestones interbedded with graptolitic shale and thick beds of limestone breccia and conglomerate. The lithology, limestone petrography, and trace fossils indicate deposition on a submarine slope of a slowly submerging carbonate platform. The limestone bed containing Arenicolites probably represents a period of slow deposition. The steeply inclined U-shaped burrows are assumed to have been formed by polychaete worms of the family Mochtyellidae which thrived in an argillaceous carbonate mud bottom of a carbonate platform slope, in depths exceeding 200 m. Although Arenicolites is believed to denote a shallow-water environment, its presence in the Cow Head extends the ecological niche of the Arenicolites-producing organisms into the outer shelf and continental slope. The domichnia of suspension feeders thus extends from shallow- to deep-water environments. 相似文献
19.
Alberto Pérez-López Angel C. López-Garrido Ana Márquez-Aliaga Carlos Sanz de Galdeano Francisco J. García-Tortosa 《Facies》2003,48(1):1-7
Summary The Cabo Cope Unit, which outcrops east of Aguilas (Murcia), belongs to the Maláguide tectonic Complex (Betic Internal Zone)
and displays stratigraphic characteristics of particular interest, including Triassic bioclastic carbonate beds which are
not common in the Maláguide units. Biostratigrafic fossils have been found in these beds and may correlate with Triassic alpine
biofacies. Alpine fauna fossils only appeared in those palaeogeographic units of the Internal Zone of the Cordillera referred
to as Alpujárride units, while the influence of the Sephardic faunal province is evident in almost all the cordillera. For
these reasons it is noteworthy that new alpine fauna fossils have been found in an Internal Zone unit in which relevant fossils
rarely appear. The Triassic succession of the unit studied in this paper can be subdivided into two members: a lower one,
which is clastic and contains thick gypsum beds, and an upper one, consisting of carbonate rocks. The lower member has been
interpreted as a fluvial-coastal deposit. The upper member is interpreted as a sequence of carbonate ramp deposits. This ramp
evolved into a shallow platform with tidal flats typical of a coastal zone. The bivalve fossilsDaonella cf.lommeli (Wissmann) and “Posidonia” sp. have been found in the carbonate member, along with the conodontSephardiella mungoensis (Diebel). These fossils are of the Late Ladinian age and have been found only in this outcroup of the Betic Cordillera. The
presence of this fossil assemblage, which belongs to the alpine faunal province, indicates a connection during the Late Ladinian
between the Tethys sea and this area of the Maláguide palaeogeographic domain. The palaeogeographic location of the Cabo Cope
Unit during the Middle Triassic was at the south-easternmost part of the Betic Basin, implying that the connection between
the Tethys and the Betic Basin was established in the easternmost domains of the basin. 相似文献
20.
《Palaeoworld》2015,24(3):336-358
The Asmari Formation in Marun oilfield (south-west Iran), is about 440 m-thick marine carbonate succession with subordinate siliciclastic rocks, characterized by abundant benthic foraminifera (perforate and imperforate). Foraminiferal biostratigraphy indicates that this unit is Oligocene–Miocene in age. The distribution of benthic foraminifera and other components have led to the recognition of three siliciclastic and ten carbonate facies that were deposited in inner ramp (shoreline, tidal flat, restricted and open lagoon and shoal), middle and outer ramp sub-environments. Based on vertical facies trends, three third-order sequences in the Oligocene and three third-order sequences in the Miocene sediments have been identified. These depositional sequences are bounded by both type 1 and type 2 sequence boundaries. The transgressive systems tracts (TST) of sequences show deepening-upward facies trend with a gradual upward increase in perforate foraminifera, whereas the highstand systems tracts (HST) have a shallowing-upward facies trend and contain predominantly imperforate foraminifera. Deposition of these depositional sequences (DS) were controlled by both eustasy and tectonic subsidence. 相似文献